The present invention relates to a method for prevention of reduction with elapse of time in nitrile hydration activity of nitrile hydratase produced by a microorganism of the genus Pseudomonas and for stable preservation of this activity.
In recent years, the technology of immobilized enzymes and microorganisms has developed rapidly, resulting in increasing attempts to utilize microorganisms and enzymes as they are or in the immobilized state as catalysts for various single or complex chemical reactions.
Nitrile hydratase was discovered by Hideaki Yamada, one of the present inventors, et al., as an enzyme capable of hydrating nitriles to produce the corresponding amides. (Reference: Agric. Biol. Chem. 46, 1165-1174 (1982)) As one example of the utilization of this enzyme, a method for producing from C.sub.2-4 nitriles the corresponding amides with the use of Pseudomonas microorganisms which produce nitrile hydratase has been proposed. (References: U.S. Pat. No. 4,637,982 and Agric. Biol. Chem. 46, 1183-1189 (1982))
As a result of further investigation, we have found that the nitrile hydration activity of the above-mentioned nitrile hydratase is labile and decreases with elapse of time. This decrease occurs in either case where the nitrile hydratase stays in microorganism cells or is separated from the cells irrespective of whether or not immobilization is effected, but the separated enzyme shows a greater reduction in nitrile hydration activity and even becomes quite unusable within a short period of time when the reduction is drastic.